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Queen bumblebees are emerging too early from hibernation

When spring arrives and the ground begins to warm up, bumblebee queens – the only bumblebees that survive the winter – emerge from hibernation and spend a couple of weeks looking for places to lay their eggs and start a new colony. However, a research team led by Lund University in Sweden has recently found that, as a result of a warming climate and a changing agricultural landscape, queens are flying earlier in the year.

The researchers found that on average, the first flight after hibernation now occurs five days earlier than two decades ago. This change may lead to the loss of various bumblebee species, reducing the pollination of crops and wild plants.

“Across Sweden, we see that the increased temperatures due to climate change clearly affect when the queens wake up and fly to find a new nest,” said study lead author Maria Blasi Romero.

However, it is not only temperature that affects bumblebees’ behavior. By using the Lund Biological Museum’s collection to examine bumblebee queens over the past 117 years in various areas of southern Sweden, the scientists discovered that the first bumblebee flight in an intensively farmed landscape occurs two weeks earlier than a century ago.

A consistent loss of grassland habitats, such as meadows and permanently grazed pastures, along with the emergence of large agricultural fields where only a few different crops are grown, has led to a general decline in farmland biodiversity. Thus, bumblebee queens leaving their hibernation earlier nowadays is likely due to a combination of rising temperatures, lack of food during the flight period, and more varying microclimatic conditions in today’s agricultural landscape than in the more diverse landscapes from a few decades ago.

By examining ten bumblebee species, the experts found that those known to fly earliest in the season have become even earlier flyers, while those emerging later in the season have not significantly changed their flight behavior. This phenomenon could lead to a poor match between the activity periods of flowering plants and bumblebees and lack of proper nourishment for several bumblebee species.

“We see a clear risk that more bumblebee species are at risk of extinction locally, especially the species that usually emerge later in the summer. This could also lead to a decline in the number of bumblebees overall and that would have consequences for the pollination of crops and the functioning of ecosystems,” said study senior author Anna Persson.

According to the scientists, some measures that could reduce the effects of climate change on pollinators and increase their access to flowering plants include preserving natural grasslands, late season mowing at roadsides (after the flowering period), and designing flower strips and hedges in ways that favor pollinators.

The study is published in the journal Biodiversity and Conservation.    

By Andrei Ionescu, Staff Writer

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